This disclosure relates to electronic circuitry such as integrated circuits (“ICs”), and more particularly to including on ICs circuitry for enabling the IC to perform (or at least facilitate the performance of) tests of the IC and/or other circuitry connected to the IC.
The increasing complexity of ICs increases the difficulty and expense of testing the performance of an IC with test equipment that is external to the IC. For example, not all points in an IC that it may be desirable to test may be sufficiently connected to an input/output pad or other similarly convenient externally accessible electrical connection attachment point of the IC. This can lead to a need for expensive, delicate, and difficult-to-use probes for accessing desired sites in the IC. A particular area of concern in this regard is the circuitry that is provided on many ICs for transmission and/or reception of high-speed serial data signals (e.g., serial data signals having serial data bit rates of about 1 gigabit per second (“1 Gbps”) or more). Such circuitry typically requires several closely coupled circuit components, some of which may be controllably adjustable, and any of which may be a source of inadequate performance of the overall transmission or communication link or system (e.g., unless properly adjusted or calibrated). As will be demonstrated in subsequent sections of this disclosure, giving an IC the “on-board,” “on-chip,” or “on-die” ability to perform or at least support certain circuit test functions, especially in the high-speed serial data signal transmission area, can be very advantageous.